AirSpaceMag.com

The Electric Airplane

Quiet, smooth, dependable—shouldn’t we be flying these by now?

It’s just 55 miles from my home airport in Los Angeles to the Tehachapi gliderport where Pete Buck has his hangar, but it’s usually a jarring flight through torrents of wind that tumble eastward off the mountains like whitewater. Not today. The air is perfectly still. The hundreds of huge windmills that dot the ridges are motionless, the sky is without clouds, the visibility without limit. I’ve pulled the rpm way back, so that the grumble of the engine, through earplugs and a headset, recedes into the distance. The airplane seems to slide along frictionlessly, like a skater coasting, hands in pockets, on a pond of infinite blue.

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An engineer with a youthful manner and a day job at the Lockheed Martin Skunk Works, Buck, 51, is waiting on the ramp when I taxi in. As we walk to his hangar, only our voices, and the occasional chirp of a bird, disturb the universal calm.

I’ve come to talk with Buck about a novel airplane he’s developing. It’s an electric airplane—common enough in RC modeling, but still an oddity in the passenger-carrying world. Electric flying is going to be something like my flight this morning: not trying to get somewhere far off in a hurry, but just the beautiful sensation of being suspended in the air, of flight for its own sake. It’s often said that every great advance in aviation begins with a new kind of engine; I suppose that putting electric motors into airplanes is such an advance, but in a somewhat backward direction: toward lower power, slower airplanes, less noise and stress, and a return to those jolly early days when merely to rise up into the air made you feel like some sort of god.

Electric flight goes back surprisingly far. In the 1880s a couple of French army officers named Renard and Krebs gave a hydrogen-filled dirigible, La France, huge batteries and an 8-horsepower electric motor that enabled it to do what no balloon had done before: return to its launch site at the end of a flight.

After that early triumph, however, all went quiet on the man-carrying electric-aircraft front and remained so for about 90 years. The current renaissance began with Robert Boucher, who pioneered the use of electric motors for model airplanes and in the early 1970s built a couple of pilotless solar-powered aircraft under contracts with the Defense Advanced Research Projects Agency. In 1979, the late Paul MacCready, whose Gossamer series of human-powered airplanes had brought him international fame, began working with Boucher. MacCready’s company, AeroVironment, first tested an electric version of the piloted Gossamer Penguin, then went on to build Solar Challenger, whose two tandem wings were covered with more than 16,000 solar cells. Boucher’s company, AstroFlight, whose principal business today is miniature motors and related gear for RC modelers, supplied the five-horsepower motor. Solar Challenger had no batteries; it collected sufficient energy from sunlight—4,400 watts—to take off, climb to 14,000 feet, and cruise at 40 mph. In 1979 it made a five-hour, 170-mile flight across the English Channel, consuming no fuel whatever. Today it resides, deservedly, in the Smithsonian.

AeroVironment later built a series of ever-larger, unmanned solar-powered airplanes, culminating in the 247-foot, 14-motor flying-wing Helios, which, when it flew, resembled a phalanx of semi-inflated air mattresses bobbing on rough water. The eventual aim of the project was to circle for days as a sort of low-level observation or communications satellite, collecting and storing sufficient energy during daylight hours to sustain itself through the night. AeroVironment was never quite able to achieve that goal; the latest iteration in its long-running quest for “eternal flight,” Global Observer, is powered by a hybrid system in which a highly efficient hydrogen-burning reciprocating engine drives a generator that in turn powers four electric motors. It is expected to be able to remain aloft for five days, in part because hydrogen has three times as much oomph, per pound, as gasoline. But the idea of an airplane that consumes no fuel continues to intrigue experimenters and adventurers; in Switzerland, one team has just crossed the Alps on solar power alone, and another has announced plans for an airplane, Solar Impulse, that is intended to circle the globe.

When Pete Buck “started poking at an electric airplane,” as he puts it, he visited the same man Paul MacCready turned to: Robert Boucher at AstroFlight. “He mentored me in the design of the motor,” says Buck, who, besides working at Lockheed Martin, is the chief engineer of Sonex, an Oshkosh, Wisconsin aircraft kit manufacturer. Buck and Sonex founder John Monnett are working on an electric conversion for one of the company’s kits, an aluminum, V-tail two-seater called Waiex (pronounced “Y-X”). Replacing a gasoline engine with an electric motor and some batteries sounds like a simple matter—those are familiar technologies, after all—but it turns out to be harder than it looks.

The project began a decade ago, when Buck and Monnett tossed around a whimsical idea for an electric airplane they called Flash Flight. It would have stayed aloft for 10 minutes on a bunch of D cells, and might have had potential for an ad campaign. Today, Buck dismisses it: “We finally decided it was silly, and it wouldn’t work anyway.” But he had caught the electric bug. He and Monnett outlined a more ambitious project: a genuine airplane, one that could stay aloft at least 20 minutes and, preferably, an hour and a half.

Their electric motor, a small cylinder bristling with cooling fins, is typical of the class of motor suitable for aviation: a 270-volt, 72-hp brushless DC unit with samarium-cobalt rare-earth magnets—the kind you would need a chisel to pry off your refrigerator door.

Magnetic forces—attraction and repulsion—cause the rotor (an electromagnet) of an electric motor to spin. Some types use two metal tabs, or brushes, with opposite charges; during each revolution, the rotor comes into contact with first one brush, then the other, each time switching its polarity. To perform the same function, a brushless electric motor relies on a solid-state switching device called a controller. Rapid switching of high-voltage currents, however, turns out to be difficult. The currents have momentum, just like moving water, and a random surge can quickly vaporize even quite massive transistors. Another problem is more mundane: The motors are hard to start.

“The controller is really where it’s at,” Buck says. “It should be cookbook, but it’s not that easy. None of us recognized the complexity. There are only a few people who know how to do it, and they aren’t talking.”